1. Field of the Invention
The present invention relates to a communication system which includes at least one radio base station to which radio network terminating facilities can be connected, wherein additional wireless communication relations via which information can be switched directly between the network terminating facilities are provided between the network terminating facilities.
2. Description of the Prior Art
In wireless communication networks based on radio channels, especially in point-to-multipoint radio feeder networks (also called “radio in the local loop” or “RLL”) a number of network terminating units are, in each case connected to a base station (also called “radio base station” or “RBS”) via one or more radio channels. In telecom Report No. 18 (1995), Vol. 1 “Drahtlos zum Freizeichen”, (wirelessly to the ringing-tone signal), page 36, 37, for example, a wireless feeder network, also called subscriber access network, for wireless voice and data communication is described. The communication system described represents an RLL subscriber line in combination with modern broadband infrastructure, e.g. “fiber to the curb”, which can be implemented within a short period of time and without great expenditure, instead of running wire-connected subscriber lines. The network terminating units RNT allocated to the individual subscribers are connected to a high-level communication network, for example to the ISDN-oriented fixed network, via the “radio channel” transmission medium and the base station RBS.
In EP 0 689 303 A, a wireless TDMA-oriented communication system is described in which a number of wireless communication terminals or mobile telephones are connected to a radio base station. The wireless communication system represents a wireless TDMA-oriented communication network in which first information items can be exchanged between the wireless communication terminals and the radio base station in accordance with a time-slot-oriented or TDMA-oriented transmission protocol. In this arrangement, this information is transmitted via a first transmission frequency. In addition, other information items modulated on a second carrier wave with a second carrier frequency can be transmitted directly between two wireless communication terminals. The additional information is then transmitted in accordance with the same TDMA protocol in accordance with which the first information items are also transmitted.
Furthermore, a communication system having at least one radio base station with mobile radio telephones connected thereto is described in which first communication relations between the radio base station and the mobile radio telephones are provided. The mobile radio telephones are designed in such a manner that direct communication with a further mobile radio telephone of the same type of construction is, in each case, possible without involving the mobile radio network. Direct communication between the mobile radio telephones takes place either via additional frequencies or via special coding methods, the direct communication between two mobile radio telephones only being possible if these are arranged spatially close enough to one another. The additional communication relations which is thus made possible between two mobile radio telephones can only be set up as direct connections between two mobile radio telephones “in the manner of a walkie-talkie”.
The present invention is directed to expanding current wireless communication networks based on a hierarchical structure, especially wireless subscriber access networks, by additional features and possible applications which are of interest both to the user and to the communication network operator.